I take some interest in the old debate about contingency and some aspect of determinism in evolutionary processes. Basically the debate is whether the basic morphology and mechanism of life on earth would exhibit the same patterns we see around us today if we rewound the clock. Stephen Jay Gould, most extensively in The Structure of Evolutionary Theory, argued for radical contingency. In Life’s Solution Simon Conway Morris takes a very different view. From what I can tell Richard Dawkins actually takes a somewhat middle perspective, though generally he is chalked up in the anti-Gouldian position (see The Ancestor’s Tale).
But ultimately this is all jaw-jaw. Real science deals in facts adduced and theories propounded. The great “debates” between “schools” of thought in the natural sciences usually suggests to me a paucity of data and method for the purposes of analysis. When it comes to contingency and inevitability that’s changing. Though I usually focus on the molecular evolutionary aspects of the scholarship (see Joe Thornton’s work), a new preprint in biorxiv utilizes phylogenetic reconstruction to indirectly addresses this question, Temporal Niche Expansion In Mammals From A Nocturnal Ancestor After Dinosaur Extinction:
Most modern mammals, including strictly diurnal species, exhibit sensory adaptations to nocturnal activity, thought to be the result of a prolonged nocturnal phase or ‘bottleneck’ during early mammalian evolution. Nocturnality may have allowed mammals to avoid antagonistic interactions with diurnal dinosaurs during the Mesozoic. However, understanding the evolution of mammalian activity patterns is hindered by scant and ambiguous fossil evidence. While ancestral reconstructions of behavioural traits from extant species have the potential to elucidate these patterns, existing studies have been limited in taxonomic scope. Here, we use an extensive behavioural dataset for 2415 species from all extant orders to reconstruct ancestral activity patterns across Mammalia. We find strong support for the nocturnal origin of mammals and the Cenozoic appearance of diurnality, although cathemerality (mixed diel periodicity) may have appeared in the late Cretaceous. Simian primates are among the earliest mammals to exhibit strict diurnal activity, some 52-33Mya. Our study is consistent with the hypothesis that temporal partitioning between early mammals and dinosaurs during the Mesozoic led to a mammalian nocturnal bottleneck, but also demonstrates the need for improved phylogenetic estimates for Mammalia.
The results from this analysis aren’t revolutionary. Through fancy rjMCMC they infer a posterior probability of 0.74 for the nocturnal hypothesis. As someone who knows very little about this topic I’d probably have guessed such a number. But at least the discussion is happening on a formal basis.
But first, this analysis highlights the likelihood that the tens of millions of years our mammalian ancestors spent as nocturnal creatures still redound to non-nocturnal lineages today, over 60 millions years beyond the end of the Age of Dinosaurs. Presumably in all this time mutation could have random-walked itself into some other optimum and moved beyond those nocturnal adaptations, but it seems that that legacy is with us still. Strike one for contingency.
Without knowing anything I’d predict birds would be the opposite, with nocturnal lineages derived from diurnal ancestors.
A final gripe about this preprint: data and code are available after publication. This is really a methods based paper and I did toy with the idea of trying to reanalyze the data. Oh well, I guess not.